Janet, that's anger is a perfectly natural reaction. My husband still drives, and should be able to do so for some time in familiar circumstances, but has gotten to the point where any road closure, etc makes him quite irritated. He also refuses to signal when he wants to change lanes, saying the other drivers won't let him in anyways -drives me crazy to go past our exit and backtrack because he is so stubborn! So far, I haven't seen real unsafe moves like hesitating in traffic or missing stop signals or pedestrians, but I am ever vigilant for it as we mainly live in two metro areas with a great deal of traffic.
He is also well into telling me how to drive, where to turn, when to stop or go, but when I say one word to him, he blows up. I used to react, but I have now internalized it and deep breathe. I also tune out his endless directions, but when friends are with us, it drives them crazy.

I have lived through dementia with a number of family members, including his Dad, and am praying I am just hypervigilant, and it is not what I am seeing in him.
Stay strong and breathe deeply!
Sue